The present invention relates to detecting a mechanical interaction with respect to a position detecting device, wherein the position detecting device is configured to detect the position of a mechanical interaction by measuring electrical potential applied across electrically conducting layers.
A position sensor for detecting the position of a mechanical interaction is described in European patent publication 0 989 509, equivalent to U.S. patent application Ser. No. 09/298,172, Korean patent application number 99-40363, Japanese patent application number 11-2,513 and Australian patent application 48770/99, all assigned to the present, assignee. The position detector is configured to determine the position of a mechanical interaction. In addition, the detector is also configured to measure the extent of the mechanical interaction in which the representation of the extent of a mechanical interaction is usually made up of components representing the force of the mechanical interaction and the area, over which the mechanical interaction takes effect.
A problem with the known position detector is that the extent measurements are extremely accurate at positions away from edge of the detector. However, as positions approach the edges of the detector and particularly when positions approach corners of the detector the accuracy of the extent of the mechanical interaction measurements, becomes relatively inaccurate.
According to a first aspect of the present invention, there is provided a fabric-made position detector, having a first fabric electrically conducting layer; a second fabric electrically conducting layer, wherein said first electrically conducting layer has a first electrical contact and a second electrical contact and said second electrically conducting layer has a third electrically conducting contact and a fourth electrically conducting contact; potential applying means for applying potential across said first contact and said third contact to produce a first current and for applying a potential across said second contact and said fourth contact to produce a second current; current measuring means for measuring said first current to produce a first current value and for measuring said second current to produce a second current value; and processing means configured to produce a property value indicating a property of a mechanical interaction by processing said first current value in combination with said second current value.
According to a second aspect of the present invention, there is provided a fabric-made position detector, having a first fabric electrically conducting layer; a second fabric electrically conducting layer, wherein said first electrically conducting layer has a first electrical contact and a second electrical contact and said second electrically conducting layer has a third electrically conducting contact and a fourth electrically conducting contact; potential applying means for applying potential across said first contact and said third contact to produce a first current and for applying a potential across said second contact and said fourth contact to produce a second current; current measuring means for measuring said first current to produce a first current value and for measuring said second current to produce a second current value; and processing means configured to produce a property value indicating a property of a mechanical interaction by processing said first current value in combination with said second current value.
An advantage of said first aspect is that the accuracy of said property value is enhanced significantly by deriving a result from the combination of two measurements. Inaccuracies may still occur at edges of the device when using isotropic conducting layers.
In a preferred embodiment, the fabric-made position detector is configured such that said fabric electrically conducting layer and/or said second fabric electrically conducting layer have different conductivites in different directions. Preferably, layer conductivity of the first layer in a first direction connecting said first contact with said second contact is lower than the conductivity in a second direction perpendicular to said first direction.
The use of non-isotropic layers facilitates a more accurate analysis and modelling of layer resistivities. Consequently, in a preferred embodiment, the property value is determined by combing a reciprocal of said first current value with a reciprocal of said second current value.
According to a second aspect of the present invention, there is provided a method of detecting a mechanical interaction with respect to a position detecting device, wherein said position detecting device is configured to detect the position of the mechanical interaction by measuring electrical potentials applied across electrically conducting layers, characterised by the steps of measuring a first current when an electrically potential is applied between a first contact and a first conducting layer and third contact of a second conducting layer while disconnecting connections to a second contact of the first conducting layer and a fourth contact of said second conducting layer; measuring the second current when an electrical potential is applied between said second and said fourth contacts while disconnecting connections to said first and said third contacts; and processing said first current measurements in combination with said second current measurement to derive an output indicative of a characteristic of said mechanical interaction.